1. Field of the Invention
The present invention relates to a sheet conveying apparatus and an image forming apparatus including the same, and more particularly, to a sheet conveying apparatus which corrects the skew feed of a conveying sheet.
2. Description of the Related Art
Generally, in an image forming apparatus, the precision of a recording position (hereinafter, also referred to as “recording precision”) of an image with respect to a sheet is one of the important factors from the viewpoint of keeping the image quality. Therefore, for example, when a conveying sheet is skewed during image formation, it is necessary to correct the skewed sheet to an appropriate sheet position. In view of this, in conventional image forming apparatus, there have been proposed various sheet conveying apparatus having a skew feed correction function so as to enhance the recording precision (see Japanese Patent Application Laid-Open No. H09-183539).
For example, in the sheet conveying apparatus described in Japanese Patent Application Laid-Open No. H09-183539, a plurality of conveying roller pairs are provided in a sheet width direction orthogonal to a sheet conveying direction, and a shutter member rotatable about a rotary shaft of the conveying rollers is arranged between the conveying roller pairs. The shutter member has an abutment portion against which a sheet abuts. When the leading edge of a sheet abuts against the abutment portion, the sheet slacks due to the reaction force from the abutment portion to form a bent loop. The formation of the loop aligns the leading edge of the sheet in parallel to the sheet width direction orthogonal to the conveying direction to correct a skew feed. Then, when the shutter member is rotated, the leading edge of the sheet is nipped by a nip portion of the conveying roller pairs while being aligned in parallel to the sheet width direction, and thus the sheet is conveyed. That is, the sheet is conveyed with the skew feed thereof being corrected. By the way, in recent years, the following has been required for an image forming apparatus: further enhancement of a throughput; increase of a conveying speed of a sheet; and decrease of a distance from a trailing edge of a preceding sheet to a leading edge of a succeeding sheet (hereinafter, referred to as “sheet-to-sheet distance”). Therefore, after the preceding sheet has passed, the shutter member needs to be returned to a home position (a position in which the leading edge of the skewed sheet abuts against the abutment portion to correct a skew feed) in the shortened sheet-to-sheet distance.
Here, FIGS. 17 to 18B illustrate a shutter member 423 provided in the conventional sheet conveying apparatus. As illustrated in FIG. 17, the conventional shutter member 423 is supported rotatably by a rotary shaft 418a of conveying rollers 418 of conveying roller pairs 418, 419. As illustrated in FIGS. 18A and 18B, the shutter member 423 guides a sheet S of which a skew feed is corrected, to a nip portion of the conveying roller pairs 418, 419. After that, the shutter member 423 performs reciprocating rotation so as to pass through the nip portion again, to thereby return to the abutment position. Therefore, the minimum required sheet-to-sheet distance is a total distance of a distance D1 from a position where the trailing edge of the preceding sheet S passes by an abutment surface of the shutter member 423 to a home position where the sheet S is subjected to skew feed correction, and a distance D2 in which, during this time, the succeeding sheet S is conveyed to the home position.
Because the shutter member 423 performs reciprocating rotation so as to pass through the nip portion of the conveying roller pairs 418, 419, the distance D1 is necessarily generated, and the shutter member 423 takes a time ΔT for moving the distance D1. On the other hand, the distance D2 is a distance (ΔT×V) obtained by multiplying the time ΔT during which the shutter member 423 moves the distance D1 by a conveying speed V of the sheet S. As the conveying speed of the sheet S becomes higher, the distance becomes longer. Therefore, when the conveying speed of the sheet S is increased in the conventional sheet conveying apparatus, the sheet-to-sheet distance becomes longer, which prevents the further enhancement of a throughput.